Transistor memory circuit



Aug. 27, 1963 A. E. ELLIS, JR

TRANSISTOR MEMORY CIRCUIT Filed March 11, 1959 WMMQDQ QOQL EOD .TI www NIL nl www 3. QNIL dlellwm M ...Sl

United States Patent O i n 3,102,207 TRANSISTOR MEMORY cnrcUrr alsam Patented Aug.'v 27, 1963` ments, and utilizing common control circuitry to control all of the cells. Employment of commoncontrol circuitry,

Albert E. 1311s Jr., New York, N.Y., assigner to Bell Telephone Laboratories, Incorporated, New York, N .Y., a corporation of New York u lFiled Mar. 11, 1959, Ser. No. 798,745 14 Claims. (Cl. 307-885) Thisinvention relates to transistor memory circuits and more particularlyto those employing junction *transistors as the basic memory elements.

In telephone switching circuits `for connectingsubscriber stations to a central oice, various degrees of however, presents unique problems. i appropriate switchingof non-selected .memory cells may For instance, in

be caused by sudden changes in volt'age or current occa-0 sioned by ychanges Vof state of the selected, and` appropriately switching, cells. j

It is, therefore, yanother object of this inventionuto' i providesfor the utilization ofbasic memory cells conconcentration may be provided to reduce the total cost Y of the circuitry. That is, the number of paths actually provided to connect a given number of subscribers to fthe central station may be less by some factor than the total `number of subscribers. ,A In one switchingy system, for example, ten paths or linksto the central oticemay be .provided to handle the traic of sixty subscribers. In

such a system it is,ftherefore, necessaiyt'hat ameans be provided for determining with alacrity the linkswhich'are available for use at any instant. l

--In an electronic switching system this determination may be' accomplished by scanning-circuitry which interrogates-the state of each link. i In addition, in such an electronic lsystem it,` is necessary toA providesome fmeans for signaling the central'oicethat a certain func- Vtion is to -be performed in `relation to the customer, that is, upon hang-up, to open the link to other subscribersV or, upon a request for service or answelyto providethe i customer with a link for completing the call. This last determining and signaling function may beaccomplished i `by memory circuitry which `remembers the prior ystate of each link and upon interrogation compares that prior state 4with the` present state of the link and signalsthe central oiiice in a manner indicative of the type of change required in the interrogated link.

To this end, it' is an objectv of this invention toprovide memory circuitry which may be utilized for re` state of the individual `links of telephone switching cir,

cuitry connecting subscribers to the central oice.

In electronic switching systems `forrtelephone circuitry a portion of the -concentrating circuitryis necessarily positioned in areas remote from the central oice. i

membering the prior states and signaling the changes in` The provision of power to a myriad of remoteconcen- `mum number of independent sources. Y

'Since the memorycircuitry isto be positioned lremote from the central oiiice .and is to serve large numbers of customers, it is desirable from a maintenancefstandpoint that the complexity of the circuitry bereducedto i a minimum. The circuitry must t,lfor instance, in al receptacle, such as abox, mounted on a telephone pole.u

An overall reduction in circuit complexity is further diesirable both from a size and cost consideration. i

`It is, therefore, another object of this invention to provide memory circuitry including a minimum number of components.

. One arrangement .for attaining the last-mentioned object involves providing a minimum number of basic mem- .i

Ory cells, each cell including a minimum number of 'ele-v having .a first terminal 5 and la second terminal 6. ThisL transistor 4 may illustratively be yof a type disclosed in Patent 2,855,524 of W. Sihockley. Equated thereto is an drawing, in which:

4 d Referring now to FIG. l there 1s v trolled by common control circuitry having a minimum number of components andfor the preclusion of, in-

appropriate switching of non-selected memory cells.

Briefly, these objects are accomplished in accordance with aspects ofl this invention by a circuit which utilizes a plurality of basic memory cells associated in parallel. Each of the cellsy comprises a two-terminal PNPN junction'transistor capable of two-state operation connected in series with a transistor access switch. Connected in common to all of the memory cells at a first terminal` are set, reset, and interrogate controlling circuits for switching the l,cells to each operational state and 'for determiningthe state of each of the cells. Each of the controlling circuits includes a transistor switch connected.

in series with a resistor of' a Value dependent on the amount ofv current desired for the selected control ,1"

operation.

Connected in common to all memory cells at a second lterminalare anv output amplifier, detecting means, and

a hold current supply. The hold current supply is especially advantageous in this circuit and includes a tran- Vsistor connected and biased to vprovide hold current Vto` memory cellsin the. set or ON statel Additionally, the v hold current supply is adapted to'lallow a detectable voltage excursion at the second common terminal while damping large voltage excursions thereat causedl by switching ofthe selected cells, Vand thereby preventingy inappropriate switching of nonselectedmemory cells. It is a feature of this inventionrthat a memory circuit comprises a plurality of shunt connected cells havingcommon control, circuitry.`

lIt is another Vvfeature of this inventionthat a common source vprovided to `supply current .tomaintainmemory cells in the ON state of operation is adaptedv to substantially eliminate voltage excursions which vtend to` cause erroneous pulsing of memory cells.

. Another'feature of'this'.inventionresides inthe use of basic memory cells connected to `utilize a minimum number of components and to require, a minimum of operating power.

These and other objectsand features of this inven-v tion may be better understood upon consideration of the'. i

following detailed description and -the accompanying n FIG. l is a diagram equating the `symbolism heretofore used to illustrate a twoterminal PNPN junction `transistor to the symbolism adopted herein;

FIG. 2 is a schematic representation of a circuit illus trative of this invention; and

FIG. 3 shows diagrams lof voltage versus time illustra`` v tive of the input pulses to each yof the individualcontrol portions ofthe circuit of FIG; 2.

shown in Alblock dia- 'gramr form .a two-terminal PNPN junction transistor 4 identical two-terminal PNPN junction transistor 4a shown, however, in schematic form. This transistor 4a has a rst terminal 5a `corresponding to the terminal 5 lof the transistor 4, and-a terminal I6a corresponding to the'terminal 6.

' General Description V Referring to FIG. 2 there is shown a memory circuit 10 memory including a plurality of memory cells, for instance ten (only one of which is :shown in detail) connected in parallel. Each cell includes a PNPN junction transistor y11 connected to an NPN junction transistor 1S. The transistor 11 is a two-state device which operates in a high impedance state for voltages applied thereaoross below a certain value and in :a low impedance state for voltages above that value. Once placed in the low impedance state by application `of a voltage of `greater than the aforementioned value, the transistor 11 remains in that state as long as sufiicient current is provided. The transistor 18 connected 'with each transistor r11 acts as a switch to connect that transistor 11 to the various control circuitry.

Each memory cell is uniquely associated lwith a particular link lor connection to a )control office by a scanner. The latter equipments are not shown as not essential to an understanding of the present invention. It is understood, however, that a memory cell 11 is adapted to store the prior state of the associated link and when the prior state of the link as determined by :scanning the cell and the present state of the link as determined 'by scanning the link differ, known arrangements :may be utilized to signal the central oflice and to revise the state of the cell to conform 'with the present state of the link.

The control circuitry includes three transistors 26, 37 and 42 adapted to control the voltage across the selected transistor 11 and thereby to change the operating state thereof. The transistors 26, 37 and i2` exert their various control functions by inserting impedances into the circuit to control the current therethrough.

The transistors 18, 26, 37 and y42 are all controlled in accomplishingy their various Ifunctions by input pulses such as shown in FIG. 3 which are applied to the bases of those transistors `18, 26, 37 and 42.

Connected at the output of the memory cells is a cornmon hold current supply source including a diode connected source of potential 3S adapted to maintain a cornmon output point A at a potential -greater than a first value and a transistor 50 biased to allow normal linear operation but maintain the :common point A below a second higher value of potential. The hold-current supply thus allows a small voltage excursion between said rst and second potentials at the point A to provide a detectable output but a voltage excursion less than adequate to `falsely switch the memory cells.

' To monitor the output, two transistors 62 and 72 are connected to provide amplification of the voltage excursions at the common point A.

Circuit .10 is adapted to operate in the following manner. As each link to the central office is scanned, the transistor 11 identified therewith is also scanned by operating the access transistor `18. As access is gained an interrogation pulse is applied to the selected transistor 11 by operating the interrogating transistor 26. if, then, the selected transistor 11 is in the low impedance state, a signal will be passed to the detector, 'while if the transistor .11 is in the high impedance Vstate no signal is passed thereto. The presence or absence of la signal from the circuit 10 is compared in circuitry, not shown, to the signal indicative of the state of the selected link. lf the state of the link and the transistor 11 differ, the central office may, by known arrangements, be signaled so that it may perform the necessary operation -in reference to the customers line. Further, if the signals differ at the comparison circuitry, not shown, a signal will be sent to either the set transistor 37 or the reset transistor 42 to cause that transistor 37 or `42 to operate and place the transistor 11 in the state indicative of the present state of the link corresponding thereto. The scanning circuitry then operates to permit access to the next succeeding transistor 11.

The Memory Cells Referring to FIG.'2 there is shown a memory circuit 10 comprising a plurality of two-terminal PNPN junction transistors 11, each having a first terminal 12 :and a second terminal 13. Each of the transistors 11 is uniquely associated with la link or path for connecting a subscriber to the central ofiice. The transistors 11, only one of which is shown, are each connected to a first common electrical point A by a shunt combination including a resistor 14 and `a capacitor 15 connected between the terminal `12 and the point A. Connected to point A by a diode 34 is a source of potential 35 utilized to bias all of the transistors 11. Other cells, such as cell 92 not shown in detail but identical to the one disclosed, may be connected to the common point A, by the lead 91, for instance.

Each transistor `11 is connected at its terminal 13 by a resistor v16 to a collector terminal 17 of an NPN transistor 18. Each transistor 18 has a base terminal 20 and an emitter terminal 19 lwhich is directly connected to a second comrnon point B. Other cells, such as cell 92, may be connected to the common point B, by the lead 90, for instance.

Each transistor 11 may illustratively be a type such as disclosed in Patent 2,855,524 of W. Shockley, issued October 7, 1958, lmentioned supra. Such a transistor 11 is of four-layer junction type capable of functioning in two operational states, dependent on the voltage applied thereacross :and the current therethrough. For applied voltages, below a first predetermined value, the transistor l11 operates in a high impedance region, to all purposes presenting an open circuit. For applied voltages of a value equal to or greater than the first predetermined value and requisite values of current, the transistor 11 passes through an unstable negative impedance region .and is placed in a second low impedance region of operation. The transistor 11 remains in that low impedance region as long as a current `of sufiicient amplitude is maintained therethrough. To provide such la current, a potential is maintained thereacross lof a second predetermined value much less comparatively than the value of the first predetermined potential.

Upon removal of the small sustaining or maintaining current, transistor 11 reverts to the high impedance state, and it is necessary to apply a potential equal to or greater than the first predetermined potential to again place it in the low impedance state.

The transistor 18 is adapted to act as a switch to allow access by the common control circuitry to the selected transistor 11. Each transistor 118, and thus access to each transistor 11, is controlled by positive imput pulses applied through a resistor 21 from a source, not shown, to the base terminal 20. The transistor 118 is biased by a positive potential provided by a source 22 through a resistor 23 to the collector terminal 17 and by a negative potential provided by a source 24 through a resistor 25 to the emitter terminal 19. The input pulses at the base terminal 20 are advantageously of an amplitude such as to saturate the transistor 13 and allow current to flow therethrough.

Referring now to FIG. 3 there are shown four voltage versus time diagrams illustrative of the individual input pulses applied to the various control and access portions of the circuit '10. The diagrams are identified by the portion of circuitry to which each pulse is directed, eg., access, interrogate, set and reset. The pulse identified as the access pulse is directed to the base terminal 20 of the selected transistor 18 and is illustratively two milliseconds, to allow completion of any of the control operations, explained hereinafter, which it may be desirable to perform upon the selected transistor 11.

`Referring again to FIG. 2, it is clear that each transistor 18 controls the access to a memory transistor 11. The base terminal 20 may advantageously be connected through the resistor 21 to a scanning circuit, not shown, which directs pulses to each transistor 18 of the circuit 10 in a predetermined fashion thereby to determine the order of access to each of the transistors 11. For instance, the scanning device might illustratively scan each transistor 11 in numerical order.

f terminal41 of a third control transistor 42.

sistor 42 hasan emitter terminal. 44 connected through The Control Circuilry Connected to point B for interrogating the state ofeach of the transistors 1'1 is a transistor 26 having abase terminal 127, anl emitter terminal '28 and a collector terminal 29. The collector terminal 29 is connected to: the common point B and, thus, through the transistors 18 to each memory transistor 11. The emitter terminal 28 is connected by a resistor- 30 to the source 24 to whichy the base terminal 27 is also connected by a resistor 31 and a resistor 32. A coupling capacitor 33 is connected between the resistors31 and 32 for` applying input pulses to the base terminal 27 from a source of positive pulses, not shown.

`For the opera-tion of the control circuitry it. will be assumed that access has been gained to, one of the `transistors 11 by applying a pulseto the base terminal 20 of the connected transistor 18. Upon the advent of a pulse at the base terminal 27, the transistor 26 is placed into operation inv its linear region. When the transistor 26 operates, the resistor 30 and the collector to emitter impedance of the transistor 26 areeiectively placed in parallel with the resistor allowing increased current te ilow through the selected transistor 418 and the `memory rtransistor 11 connected thereto, if that memory transistor `11 is in thelow impedance state.

Thevalue of current flow during interrogation is controlled by the value of i `the resistor and the impedance of the transistor 26 to be only slightlyv greater `than that through the selected memory stage when no control operation is performed thereon. The pulse applied at the base terminal 27 of the transistor 26 is a positive pulse such asthat identified in FIG. 43 as the interrogate pulse. The pulse is illustratively of short duration` and low amplitude maintaining the transistor 26 in the amplifying state for approximately one microsecond.

. `Another portion of control circuitry connected to point liB, includes a collector/terminal 36 of` an NPN junction transistor 37 having a base terminal 38 and an emitter terminal 39. The-emitter terminal 39 is connected to the source 24 through a resistor 40, and the base terminal is connected Ithrough a resistor 49 to a source of positive pulses, not shown, of an amplitude appropriate to saturate the transistor 37. The resistor 40 is of a value of resistance less than that of the resistor 30 suchthat upon its connection in parallel withv the resistor 25, the

. current through the selected access transistor 18 increases greatly. This portion of input `circuitry is known as the "set input `since its operation places the selected transistor 11 in the set or low impedance state, as explained hereinafter.

The input pulses applied to the base terminal`38 of the Vtransistor 37 are of a type identified lin HG. 3 as a set pulse. These pulses are of a much greater length, eig. 25 times greater, than the pulses applied to `the transistor 11 by the interrogating circuitry.

Also connected to the common point B is a collector a resistor 45 to the source 24 and a base terminal`43 connected through a resistor 46 to a source of positive input pulses," not shown. The source of pulses, not shown, furf Dishes a pulse, described in FIG. 3 as a reset pulse,A of an` amplitude great enough to saturate the transistor 42 and place the resistor 45 in parallel with the resistor 25.

The resistor 45 is of a value less thanthatof the resistor 40 -to allow greatercurrent ilowthrough the circuit 1t) during the operation of the transistor 42 than during the operation ofthe transistor 37.

The operational states of the transistorsflll arecons, trolled and interrogated bythecommon circuitry connected to the common point B which circuitry is adapted to provide' the potentials necessary across the selected trolled by the voltages provided by the source 35 and Y switching to the low impedance state. Si-ncethe voltage Y across the resistor 23 is determined by the current therethrough and that current is determined'by the total impedance of the circuitry connected thereto, the voltage across each transistor 11, in the high impedance state with no voltageacross the resistor 14, is determinedy and controlled by they Value of the impedance connected to theresistor 23 `by the various control elements. If the impedance is large, little current lflows, and only a small Voltage appears across the resistor 23 while if the impedance is small, a large current and voltage are produced.

The actual switching of the circuit 10 is effected bythe capacitor 15 connected in parallel with the resistor 14 to each transistor 11. The capacitor ifunctions in a manner described in `a copending patent application Serial No. 798,746, tiled March ll, 1959, of W. C. Jones and P. G. Ridinger, now United States Patent No. 3,021,43 6, issued February 13, 1962.y

Basically, the operation is as follows, In the high impedance state the voltage applied acrossl each transistor 11 is approxi-mately two-thirds that required for switching to the low impedance state. If a low impedance such as the resi-Stor of the set control circuitry is connected to the resistor 23, the voltage across` the selected transistor 11 and thus the current therethrough is great enough to switch the selected transistorll to the low impedance state.

During the time the resistor 40` is connected by the operation of the transistor 37, capacitor 15 ycharges to a` voltage 'determined by the duration of connection of the The trany resistance 40 and the values of the resistors 14, 16, 23, 25 and 40 to be less than that which would, upon removal of the resistor `40 romthe circuit 10, cause the current through the selected transistor 11 to fall below that necessaryfto sustain operation in the low impedance state. Thus, upon removal of the resistor 40 and the deenergizing of transistor 18, the transistor 11 remains in the low impedance state and a voltage is built up on the `capacitor 15 determined by the voltage divider action of the resistors 14, 16 and 23. Thetransistor 11 will remain in the low impedance state indenitely because the resistors 14, 16, and `23 are chosen to be of value such that sufficient sustaining current is furnished.

Upon connecting the resistor 45 to ,the resistor 23 by operating the transistor 42, the voltage -acrossthe capacitor 15 begins to build up again but from a higher initial value due to the charge already on the capacitor 15. At the release of the resistor 45, by turning -o the transistor 42, the voltage on the capacitor 15 is suliiciently great so thatthe selected transistor 11 does Anot have adequate current therethrough to sustain operation in the `low impedance state and it reverts to the high impedance state.

If, on the other hand, the resistor 30 is connected to the resistor 23 by operating the interrogating transistor 26, the changes in voltage and current are too small and the duration too short to cause switching of the -selected transistor 11. -It is to be noted from FIG. 3 that the input pulse to transistor 26 is only one-twenty-iifth as long as the pulses to transistors 37 and 42. Thus, since the voltage at the `selected capacitor 15 depends on .the `duration of current produced by the various control circuitry, the operation `of the transistor 26 is ineective to change that Voltage appreciably. This feature permits non-destructive interrogation or read-out of the condition of transistors 11, and is particularly advantageous in this type of circuit in consequence of the need for` constant and repetitive interrogation, as explained infra.

T he Hold Current Supply Connected to the common point A is an NPN transistor `50 having a base terminal 51, an emitter terminal 52 and a collector terminal 53. The emitter terminal 52 is connected to common point A, the base terminal 51 to a source of potential 55 through a resistor 54, yand the collector terminal 53 to the source 55 through an inductor 56. TIhe potentials furnished by the sources 35 :and 55 are such as to bias the transistor 50 for amplifier operation.

When any one of transistors 11 changes state there is a sudden change in the current supplied to the circuit 10. This change in current could, without compensating circuitry, cause an accompanying change in voltage at the common points large enough, instantaneously, to cause improper opera-tion of the various non-selected transistors 11 connected thereto. The transistor 50 and the source 55 are therefore provided to act in conjunction with the source 35 as a current supply for the transistors 11 in the ON state land to damp any voltage excursions of point A which might inappropriately operate non-selected ones of the transistors 11 while allowing enough voltage excursion thereat to provide a detectable circuit output.

If the circuit 10 is operating and an additional transistor 11 is switched to the low impedance state the total current through the circuit 10 increases. This increase would normally tend -to lower the voltage at point A, possibly removing sustaining potential from ON ones of the transistor 11. The source 35 Iand the diode 34, however,

`clamp the voltage `at point A so it does not fall below a value equal to that supplied by source 35, for example, as illustrated, 37 volts.

At the same time, the transistor 50, which is biased to normally operate in the amplifying region, tries to furnish some of the additional current. However, no instant current change through the inductor 56, connected to the collector 53, is possible, and a large voltage appears across the inductor 56, positive at the terminal connected to the source 55 with respect to the other terminal thereof. This voltage overcomes the back biasing voltage provided across the resistor 54 and the transistor 50' is forward biased at its base-collector junction. As the transistor t) saturates, the drop thereacross becomes negligible, and the emitter 52 takes on approximately the same potential as the collector 53. The voltage at the collector 53 is less than that furnished by the source 55, 40 volts as illustrated, by the voltage drop across the inductor 56. The voltage at the emitter 52 cannot, however, drop below the voltage furnished by the source 35 due to the clamp furnished by the diode 34. Thus a slight voltage excursion from the potential furnished by the source 55 is provided, at the common point A.

If, on the other hand, one of the transistors 11 operating in the low impedance state is switched to the high impedance state, the total current through the circuit decreases and the voltage at point A tends to increase.

As the total circuit current attempts to decrease, the current through the inductor 58 attempts to change. The attempted change of current produces a large voltage across the inductor 56, positive at the bottom thereof with respect to the top as viewed in the drawing; and this voltage, in cooperation with the voltage across the resistor terminal 54, back-biases the collector terminal 53 with respect to the base 51. Such a back-biasing effect causes the transistor 50 to operate in its linear amplifying region wherein the currents from the various terminals are controlled by the values of the current at all the other terminals. Since the collector current remains constant instantaneously, so must the base current which is a constant fraction thereof. And since the -base current remains constant, the voltage across the resistor 54 remains constant. In the linear region, there is no appreciable drop between the Ibase and emitter terminals of a transistor because of the forward biasing applied thereto. Thus, since the transistor 50 is biased for normal amplier operation and it remains in that state, the emitter terminal '52, due to `forward biasing of the emitter and base terminals 52 and 51, is at and remains at the same voltage as the base terminal 51, or slightly less than the 40 volts supplied by the source 55.

As the current through the inductor 56 reduces eX- ponentially the current through the resistor 54 reduces in the same manner. At all times, however, the voltage at the emitter terminal 52 remains approximately the same as that at the base terminal 51 thus, below 40 volts as long as the transistor 50 is in the linear condition since there is always some drop across the resistor 54 as long as current flows therethrough.

Thus the point A is clamped to -a small excursion (between the levels of sources 35 and 55) of approximately 3 volts which has been found to be great enough to produce a detectable output yet not great enough to cause improper switching of the transistors 11.

The Output Crcutry When the interrogating operation is performed by operating the transistor 26 to determine the state of the selected transistor 11, the 3-Volt excursion allowed at point A provides 'a means for detecting the state of that transistor 11. Operating the transistor 26 causes a slight increase in the current through the circuit 10 and yan accompanying slight drop in voltage at point A.

As point out, supra, vapplying a pulse, as shown in FIG. 2 to the base terminal 27 of the transistor 26 after transistor 118 is energized inserts a smaller impedance in the circuit between point B and the source 24 than was present theretofore. Reducing the impedance reduces the voltage therebetween. If the selected transistor 11 is in the high impedance state, the change in voltage is so small compared to the total voltage Kbetween points A and B, that it is negligible. If, however, the transistor 11 is in the low impedance state the voltage change amounts to some slight but detectable value and a negative-going voltage pulse is realized at point A.

Connected to the common point A is a capacitor 60 which is of la Value such las to couple the aforementioned negative pulse to a base terminal 61 of an NPN junction transistor 62. The transistor 52 has an emitter terminal 63 and a collector terminal 64. The emitter terminal 63 is biased by a negative source of potential 65 through a resistor 66, the `collector terminal by a positive source of potential 67 through a resistor 63, and the base terminal 61 by a negative source of potential 69 connected thereto by a resistor 70. The values of the potentials furnished by the source `65, 67 and 69 =are such as to place the transistor 62 in its linear operating region.

As may be seen, a negative pulse at the base terminal `61 tends to `decrease the current through the transistor 62 thus increasing the potential thereacross and raising the voltage at the collector terminal 64. This, in effect, inverts and iamplies the negative input pulse and applies it `as a larger positive pulse to a base terminal 71 of an NPN junction transistor 72.

The transistor 72 has an emitter terminal 73 connected to :a source of negative potential 75 through a resistor 76 and a collector terminal 74 connected to ground. In addition, a capacitor 77 is connected to the emitter terminal 73 and to a diode 79, and `a resistor 78 is connected between the diode 79 and the capacitor 77 and to the source 75. These connections bias the transistor 72 for linear operation `so that when the inverted land amplified pulse is received at the base terminal 71 as a positive pulse, increased current flows through the transistor 72 producing a positive potential at the emitter terminal 73 with respect to the potential furnished by the source 75 Idue to the voltage across the resistor 76. This positive voltage pulse is repeated by the capacitor 77 rand the resistor 78 through the diode 79 to a detecting circuit, not shown, where comparison is made with the present state of the `associated link to `determine whether subinterrogating pulse to prevent any undesired `when it is in the `high impedance state. The means for determining the prior states ofthe transistors 11 is therefore furnished by this circuit 410.

The detector circuitry, not shown, is inhibited after the signals due to"set or reset pulses. t i t As mentioned supra, the output or lack of output signal realized by pulsing the base terminal 27 and thereby energizing the interrogating transistor 26, when the selected transistor 11 has been connected thereto by operating the selected access transistor 18, is compared with a manner, `by operating the interrogating transistor 26 and the corresponding access transistor :18.`

` The parameters of the elements of the embodiment of FIG. 2 may advantageouslytake the following illustrative values:

PNPN transistors .11:

It is to be understood that the above-described arrangement is illustrative of the application of the principles of this invention. devised by those skilled in the art without departing from the spirit and scope of the invention.

What is claimed is:

1. Aniemory circuit comprising a plurality of bistable memory cells connected in parallel each including an input terminal, an output terminal, an access means for selecting predetermined ones of said cells; common set, reset, and interrogating means connected to said input terminals of said cells for providing pulses to selected ones of said cells; common output means including amplifying means connected to said output terminals of all of said cells; and common hold-current-supply means including a tirst source of potential, unidirectional current means connecting said iirst source of potential and said output terminals to maintain said output terminals at Ia potential greater than the potential supplied by said first source, and a transistor amplifier comprising a transistor having base,

t signal indicative of the state of the link corresponding to f the selected transistors 11. df. the statesof thelink and Breakdown voltage volts f-c Sustaining current ma-- @l t Transistor .18 WE 2N560 YTransistor 26 WE ZN560 Transistor 37 WE 2N560 Transistor 42 WE 2N560 Capacitor 15 ptf 0.01 Capacitor 33 ;1.f 0.003 Capacitor at 0.01 Capacitor 77 ;rf 0.01 Inductor 56 mh 15 Diode 34 'i WE 2030 Resistor -14 ohms 5.6K Resistor` 16 do 1.2K Resistor 21 do 560 Resistor 23 do 6.8K Resistor 25 do 3.9K Resistor 30 do 3.9K Resistor 31 do `8.2K Resistor 32 do 8.2K Resistor 40 do 1.8K Resistor 45 do Resistor 46 do 560 Resistor l49 do 3.6K Resistor 54 do 560 Resistor 66 do 1.5K Resistor 68 do 15K Resistor 70 do 3K Resistor 76 do 10K Resistor 78 do 10K .Numerous other `arrangements may be i 10 emitter, land collector electrodes; a second source of potential greater than the potential supplied by said first source, 1an inductor connecting said collector electrode to said second source, a resistor connecting said base eleci trode to said second source, and means connecting said emitter electrode to said output terminals whereby the potential at said output terminals is maintained at avalue less than the value of the potential supplied by said second source.

2. A memory circuit comprising a plurality of `twostate devices, each of said devices having a first and a second terminal; a plurality of charging means, each of said charging means connected to said tirst terminal of individual ones of said plurality of devices and'at a common point to all the others of said ch-arging means; a iirst source of potential connected by unidirectional current means `to each of said charging means `at said common point; a `first, a second and a third impedance; a second source of potential connected to Iall of said impedances; switching means for individually and noncoincidentally connecting each of said impedances to a selected one of said plurality of devices at said second terminal thereof; output means connected to all of said plurality of charging means at said common point including a third source of potential for maintaining the voltage thereat below a predetermined value and including amplifier means for detecting a change in voltage at said common point.

3. A memory circuit as in claim 2 wherein said output means includes a transistor amplifier comprising a transistor having base, emitter, and collector terminals, said collector terminal inductively coupled to said third source of potential, said base terminal resistively connected to said third source of potential, and said emitter terminal connected fto said common point.

4. A memory circuit as in claim 2 wherein said output means further includes a transistor regulator inductively coupled to said third source of potential and connected to all of said charging means at said common point.

5. A memory circuit as in claim 4 wherein each of said charging means includes a resistor and a capacitor connected in parallel.

6. A memory circuit as in claim 4 wherein said ampliiiter me-ans includes a rst ampliiier having an input terrninal capacitively coupled to said common point, and an output terminal; Iand a second amplifier having an input terminal connected to said output terminal of said iirst amplifier, andan output terminal.

7. A memory circuit as in claim 6 wherein said iirst and second ampliers comprise transistor amplifiers connected in driving and driven relationship to operate as an amplier-inverter.

8. A memory circuit asin claim 4 wherein said switching me-ans includes transistor switches for connecting each of said impedances to each of said devices.

9. A memory circuit as in claim 4 wherein each of said `devices includes a two-terminal PNPN junction transistor.

l0. A memory circuit comprising a plurality of twostate devices, each of said devices having a rst and a second terminal; a plurality of charging means, each of said charging means connected to said iirst terminal of individual ones of said plurality of devices and at a common point to all the `other of said charging means; a first source of potential connected by unidirectional current i means to each of said charging means at said common point; a second source of potential; switching means for connecting said second source of potential to a selected one of said plurality `of devices at said second terminal thereof; output means including a third source of potential and a transistor having a base, a collector and an emitter, said base resistively connected to said third source, said collector inductively connected to said third source, and said emitter connected to all of said plurality of charging means at said comm-on point for maintaining the voltage thereat below a predetermined value.

11. A memory circuit as in claim 10 including interrogating means for interrogating each of said two-state devices, said interrogating means including a transistor connected to said switching means, and a resistor connected to said transistor, said transistor being operable to connect said resistor to said switching means to determine a rst of a plurality of current levels therethrough.

12. A memory circuit as in claim 1l including setting means for placing each of said two-state devices in a rst operation state, said setting means including a transistor connected to said switching means, and a resistor connected to said transistor said transistor operable to connect `said resistor to said swtiching means -to determine a second of said plurality of current levels therethrough.

13. A memory circuit as in claim l2 including resetting means for placing each of said two-state devices in a second operation state, said resetting means including a transistor connected to said switching means, and a resistor connected to said transistor, said transistor operable to connect said resistor to said switching means -to determine a third of said plurality current levels therethrough.

14. A memory circuit as in claim l0 wherein said switching means includes a plurality of transistors, each of said transistors connected to one of said two-state devices and to said second source, said memory circuit further including iirst, second, and third impedances and means for connecting each of said impedances to each of said plurality of transistors to respectively interrogate, sett and reset said devices by changing the current therethrough, said rst impedance being of a greater value than said second impedance, and said second impedance being of a greater value than said third impedance.

References Cited in the file of this patent UNITED STATES PATENTS 2,693,572 Chase Nov. 2, 1954 2,779,877 Le Hovec Jan. 29, 1957 2,801,296 Blecher July 30, 1957 2,805,397 Ross Sept. 3, 1957 2,862,175 Guyton Nov. 25, 1958 2,880,331 MacSorley Mar. 31, 1959 2,897,431 Wolfendale July 28, 1959 2,902,642 Voegtlen Sept. 1, 1959 2,902,674 Billings Sept. 1, 1959 2,906,891 Scanlon Sept. 29, 1959 2,907,000 Lawrence Sept. 29, 1959 2,913,594 Eckert Nov. 17, 1959 

1. A MEMORY CIRCUIT COMPRISING A PLURALITY OF BISTABLE MEMORY CELLS CONNECTED IN PARALLEL EACH INCLUDING AN INPUT TERMINAL, AN OUTPUT TERMINAL, AN ACCESS MEANS FOR SELECTING PREDETERMINED ONES OF SAID CELLS, COMMON SET, RESET, AND INTERROGATING MEANS CONNECTED TO SAID INPUT TERMINALS OF SAID CELLS FOR PROVIDING PULSES TO SELECTED ONES OF SAID CELLS; COMMON OUTPUT MEANS INCLUDING AMPLIFYING MEANS CONNECTED TO SAID OUTPUT TERMINALS OF ALL OF SAID CELLS; AND COMMON HOLD-CURRENT-SUPPLY MEANS INCLUDING A FIRST SOURCE OF POTENTIAL, UNIDIRECTIONAL CURRENT MEANS CONNECTING SAID FIRST SOURCE OF POTENTIAL AND SAID OUTPUT TERMINALS TO MAINTAIN SAID OUTPUT TERMINALS AT A POTENTIAL GREATER THAN THE POTENTIAL SUPPLIED BY SAID FIRST SOURCE, AND A TRANSISTOR AMPLIFIER COMPRISING A TRANSISTOR HAVING BASE, EMITER, AND COLLECTED ELECTRODES, A SECOND SOURCE OF POTENTIAL GREATER THAN THE POTENTIAL SUPPLIED BY SAID FIRST SOURCE, AN INDUCTOR CONNECTING SAID COLLECTOR ELECTRODE TO SAID SECOND SOURCE, A RESISTOR CONNECTING SAID BASE ELECTRODE TO SAID SECOND SOURCE, AND MEANS CONNECTING SAID EMITTER ELECTRODE TO SAID OUTPUT TERMINALS WHEREBY THE POTENTIAL AT SAID OUTPUT TERMINALS IS MAINTAINED AT A VALVE LESS THAN THE VALVE OF THE POTENTIAL SUPPLIED BY SAID SECOND SOURCE. 